Estimation of Pre-stress on Under-cored Sandstone Samples

• Main Authors: Yu-Wei Pan, 潘昱維
• Other Authors: Jian-Hong Wu
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/40817429106677775156

碩士 === 國立成功大學 === 土木工程學系碩博士班 === 97 === As the increasing of size and depth of the tunnel constructions in Taiwan, measuring the pre-stress of the rock mass is an essential task for the tunnel design. For example, the maximum overburden thickness of the Tseng-wen reservoir tansbasin water tunnel is roughly 1300m, and the in situ stress condition will affect the design and safety. Therefore, it is necessary to develop an easy and economical technique to assess the in-situ stresses. The diameter of rock core samples taken from in situ borehole drilling is usually 5cm. In stead of conducting borehole drilling from different directions, in this study, we take under-cored samples at various directions from oriented rock core samples and integrate to the laboratory experiments (acoustic emission and deformation rate analysis) to analyze the in-situ three-dimensional stresses. To realize the stress memory characteristics of the under-cored rock samples and the accuracy of pre-stress estimations under different directions, we chose Changchikeng Sandstone as experiment specimen, and combined the artificial prestressed under-cored samples to the acoustic emission and deformation rate analysis to estimate the stress memory characteristic of the sandstone. The following test results of laboratory experiments will contribute to estimate the in situ stress on Tseng-wen reservoir tansbasin water tunnel region in the future. 1.High pre-stress loaded samples result in unstable crack activities. The number of loading cycles may affect the measuring results. It is appropriate that triaxial pre-stress loaded simultaneously for simulating in situ three dimensional stresses. 2.The triaxial pre-stress test resulted indicate that the under-cored Changchikeng Sandstone samples also perform Kaiser Effect, and the direction-dependency. In addition, the test results also proved that over-coring samples associating with acoustic emission and deformation rate analysis are feasible for estimating three dimensional stresses. 3.Future stress estimations conducted in the Tseng-wen reservoir tansbasin water tunnel region may encounter the following problems: the correctness of the pre-stress estimation depends on the value of the in-situ stress, determination of take-off point of the Kaiser Effect, stick strain gauge on the samples, and the delay time. Thus, when pick rock core samples or carry out experiments should modify these problem.